Ink jet printing apparatus and printing method

Abstract

High image quality is maintained even on front and rear ends of a printing medium where deterioration in the image quality is more likely to occur due to reduction in conveyance accuracy of the printing medium. In printing on the front and rear ends, the printing medium being not supported by both conveying means respectively placed upstream and downstream of a printing point in a printing medium conveying direction, a print swath of a printing head and the amount of conveying a printing medium are reduced. Moreover, the reducing print swath and the reducing conveyance amount are designed to be decreased in the cases of selecting a printing medium for high-quality printing as well as a monochrome print mode where image distortion caused by deviation of ink-landing positions is more noticeable due to a small number of colors of ink to be used and low coverage thereof.

What is claimed is: 
     
       1. An ink jet printing apparatus for printing an image by performing a print scan which makes a print while causing a printing head, which includes an array of printing elements for ejecting ink, to scan on a printing medium in a direction different from a direction of the array, and by conveying the printing medium in a direction intersecting with the direction of the print scan, the apparatus comprising:
 controller which reduces a range in the array of the printing elements to be used for printing on at least one of front and rear end portions of the printing medium so that the range can be smaller than a range in the array of the printing elements to be used for printing on a central portion of the printing medium, and thus, which performs the print scan, 
 wherein the controller changes the size of the reducing range depending on at least one of a print mode selected from a plurality of print modes, each having the different number of colors of ink usable for printing the image, and a type of selected printing medium. 
 
     
     
       2. An ink jet printing apparatus for printing an image by performing a print scan which makes a print while causing a printing head, which includes an array of printing elements for ejecting ink, to scan on a printing medium in a direction different from a direction of the array, and by conveying the printing medium in a direction intersecting with the direction of the print scan, the apparatus comprising:
 controller which reduces a range in the array of the printing elements to be used for printing on at least one of front and rear end portions of the printing medium so that the range can be smaller than a range in the array of the printing elements to be used for printing on a central portion of the printing medium, and thus, which performs the print scan, 
 wherein the controller changes the size of the reducing range depending on a print mode selected from a plurality of print modes, each having the different number of colors of ink usable for printing the image. 
 
     
     
       3. An ink jet printing apparatus as claimed in  claim 2 , wherein the controller more decreases the size of the reducing range in a print mode in which the number of colors of ink usable for printing the image is a first number relative to a print mode in which the number of colors of ink usable for printing the image is a second number greater than the first number. 
     
     
       4. An ink jet printing apparatus as claimed in  claim 2 , wherein:
 the printing head has an array of the printing elements ejecting achromatic ink and an array of the printing elements ejecting chromatic ink; 
 the plurality of print modes includes a first print mode in which a print is made by using mainly the achromatic ink and a second print mode in which a print is made by using mainly the chromatic ink; and 
 wherein the controller more decreases the size of the reducing range in the first print mode relative to the second print mode. 
 
     
     
       5. An ink jet printing apparatus as claimed in  claim 4 , wherein the achromatic ink is used more than the chromatic ink in the first print mode. 
     
     
       6. An ink jet printing apparatus as claimed in  claim 2 , further comprising:
 first conveying unit which conveys the printing medium, positioned upstream of the printing head in the conveying direction; and 
 second conveying unit which conveys the printing medium, positioned downstream of the printing head in the conveying direction, 
 wherein the controller performs the print scan after determining that print is to be made on the front end portion when the printing medium is supported by only the first conveying unit, determining that the print is to be made on the central portion when the printing medium is supported by both the first and second conveying units, and determining that the print is to be made on the rear end portion when the printing medium is supported by only the second conveying unit. 
 
     
     
       7. An ink jet printing apparatus as claimed in  claim 2 , wherein a marginless image is printed on at least one of the front and rear end portions of the printing medium. 
     
     
       8. An ink jet printing apparatus as claimed in  claim 2 , wherein the printing medium is conveyed by the amount less than a width of the range to be used in the print scan, and thereby, the print is made by plural times of print scans, in accordance with a mask pattern which defines a pixel arrangement having a complementary relationship in the same image region on the printing medium. 
     
     
       9. An ink jet printing apparatus as claimed in  claim 8 , wherein mask patterns are changed for making the print on at least one of the front and the rear end portions, depending on the type of the printing medium, the mask pattern being applied to the plural time of print scans. 
     
     
       10. An ink jet printing apparatus as claimed in  claim 9 , wherein:
 the pixel arrangement of the mask pattern has a distributive characteristic in which a printable rate is a maximum at the printing element of the position corresponding to a center of the array of the printing elements to be used for making a print, and in which the printable rate tends to decrease toward the printing elements of end portions of the array; and 
 the mask patterns each having different printable rates of the central portion and the end portions are used depending on the type of the printing medium. 
 
     
     
       11. An ink jet printing apparatus for printing an image by performing a print scan which makes a print while causing a printing head, which includes an array of printing elements for ejecting ink, to scan on a printing medium in a direction different from a direction of the array, and by conveying the printing medium in a direction intersecting with the direction of the print scan, the apparatus comprising:
 controller which reduces a range in the array of the printing elements to be used for printing on at least one of front and rear end portions of the printing medium so that the range can be smaller than a range in the array of the printing elements to be used for printing on a central portion of the printing medium, and thus, which performs the print scan, 
 wherein the controller changes the size of the reducing range depending on a type of selected printing medium. 
 
     
     
       12. An ink jet printing apparatus for printing an image by performing a print scan which makes a print while causing a printing head, which includes an array of printing elements for ejecting ink, to scan on a printing medium in a direction different from a direction of the array, and by conveying the printing medium in a direction intersecting with the direction of the print scan, the apparatus comprising:
 conveyance controller which reduces the amount of conveying the printing medium in making the print on at least one of front and rear end portions of the printing medium as compared with the amount of conveying the printing medium in making the print on a central portion of the printing medium, 
 wherein the controller changes the reducing conveyance amount depending on at least one of a print mode selected from a plurality of print modes, each having the different number of colors of ink usable for printing the image, and a type of selected printing medium. 
 
     
     
       13. An ink jet printing method of printing an image by performing a print scan which makes a print while causing a printing head, which includes an array of printing elements for ejecting ink, to scan on a printing medium in a direction different from a direction of the array, and by conveying the printing medium in a direction intersecting with the direction of the print scan, the method comprising the step of:
 reducing a range in the array of the printing elements to be used for printing on at least one of front and rear end portions of the printing medium so that the range can be smaller than a range in the array of the printing elements to be used for printing on a central portion of the printing medium, and 
 performing the print scan using the printing elements of the reduced range, 
 wherein in the reducing step, the size of the reducing range is changed depending on at least one of a print mode selected from a plurality of print modes, each having the different number of colors of ink usable for printing the image, and a type of selected printing medium. 
 
     
     
       14. An ink jet printing method of printing an image by performing a print scan which makes a print while causing a printing head, which includes an array of printing elements for ejecting ink, to scan on a printing medium in a direction different from a direction of the array, and by conveying the printing medium in a direction intersecting with the direction of the print scan, the method comprising the step of:
 reducing the amount of conveying the printing medium in making the print on at least one of front and rear end portions of the printing medium as compared with the amount of conveying the printing medium in making the print on a central portion of the printing medium, 
 wherein in the reducing step, the reducing conveyance amount is changed depending on at least one of a print mode selected from a plurality of print modes, each having the different number of colors of ink usable for printing an image, and a type of selected printing medium.